I want to measure a current ( the load is uknown (changes)) and a voltage, such that I can make a maximum Power point calculation. Is it possible to use a DAC, for the current and a ADC for the Voltage? If yes, how should I configured it.

I am measuring the potential (voltage) difference and current between two dissimilar metals (in a electrolyte). Is it not possible to use a DAC (sinking), to measure the current (1 to 50 uA) directly? And a ADC to measure the open circuit potential (100-800mV)?

The opamp is in differential configuration. The difference of the voltage will be proportional to the current.You can measure the current by passing it through the shunt resistor. I am not sure what you meant be measure current using DAC ? You can use the PSoC 5 IDAC to generate current upto 2.04mA, if that is what you were asking. ADC can be used to measure the voltage you are referring.